Non-invasive methods of measuring blood flow in human body organs typically involve injection or inhalation of a contrast medium, followed by generation of a series of CT images from an X-ray CT device to measure the concentration of the contrast medium in a part of the organ of interest, such as the brain. This method is described by Teeter and Colsher in "Imaging of Xenon Enhanced Cerebral Blood Flow with High Resolution CT," Radiology, Oct. 1984. An improved dynamic scanning apparatus and method for measuring the rate of build-up of the concentration of the contrast medium is described in U.S. Pat. No. 4,718,432, entitled "CT Imaging Apparatus and Method for Measuring Local Cerebral Blood Flow" by Kimura et al, assigned to the same assignee.
Generally a characteristic curve of the relative absorption of X-rays, called the CT number, is made for a region of interest (ROI) over a period of time by making multiple images. The resulting curve, an example of which is shown in FIG. 8, provides a basis to calculate the blood flow in the ROI. This technique most accurately is applied to stationary organs because motion of the ROI, such as from the beating of the heart or from respiratory movement, causes changes in contrast resulting in errors in the characteristic curve. Images and characteristic CT curves built up from several data points using standard dynamic scanning methods while the ROI is in motion result in dynamic curves unacceptable for diagnosis.
To perform an accurate dynamic scan, the collected data must be synchronized with the motion of the ROI to properly average the motion affects so that each CT number plotted is consistent with the other CT numbers.